[Milsurplus] URM25

[Paul Kraemer]

Got into a couple URM25D with an extra board mounted below the audio section behind the rf attenuator.
Board has two power resistors, two electrolytics, two top hat diodes and a stud mount diode.
I have not encountered this option before
Can anyone enlighten me what it is?  Guessing maybe dc filament supply from size of components?
I don’t find it documented anyplace I have looked
Thanks
Paul K0UYA